The group that experienced the greatest change during WWII was probably African Americans. They still served in segregated regiments in the armed forces, but more than 1 million of them answered the call to fight. And just as important, continuing the Great Migration that had begun in the 1920s, 700 thousand African Americans left the south, moving to northern and especially western cities where they could find jobs, even though these mass migrations often led to tensions between blacks and whites and sometimes these tensions exploded into violence.
WWII also saw the beginning of the Civil Rights movement. Angered by discrimination in defense employment, black laborer A. Phillip Randolph threatened a march on Washington demanding access to defense jobs, an end to segregation, and a federal anti-lynching law. He didn't get all of those things, be he did get Executive Order 8802 which banned discrimination in defense hiring and created the Fair Employment Practices Commission. The FEPC couldn't enforce anti-discrimination but as a compliance agency it helped African American workers obtain jobs in arms factories and shipyards. By 1944 more than a million black people were working in manufacturing, and 300 thousand of them were women.
The rhetoric of fighting a war for freedom against a racist dictatorship wasn't lost on African Americans, and many saw themselves as engaged in the double-V campaign, victory over the Axis powers abroad and over racism in the US.
The war saw ending segregation and black equality become cornerstones of American liberalism, along with full employment and the expansion of civil liberties. Eventually even the army and navy began to integrate, although the full end to discrimination in the military would have to wait until well after the war.